Numerous absorbent articles for use in the absorption of bodily fluids and discharges such as menses, urine, feces and the like are known. Such absorbent articles have incorporated elastic components to improve the fit of the article. For example, U.S. Pat. No. 4,978,570, issued to Heyn, et al. on Dec. 18, 1990 is directed to a disposable diaper having an elastic waist provided with a foam strip to cushion stresses of the elastic waistband in the waist area. The composite waistband consists of an elastomeric strip and a foam strip. The use of a foam tends to provide desirable properties in the article, e.g., compressibility, resilience, and/or thickness. However, such articles suffer from the disadvantage that the foam requires an external bonding agent to construct the article which adds to the cost of the article. In addition, such foams generally must be cut to fit the article as desired such that waste may be generated, thereby further increasing the cost of the articles incorporating the foam. Finally, foams such as the polyurethane foams disclosed therein are prepared on a separate line for later incorporation into the article. This need to prefabricate the foam also adds to the cost of the article.
Other prefabricated foams have been used in the art, e.g., natural rubber foams. In addition to the disadvantages of the need to prefabricate the foam, cut the foam to fit, and to use an external bonding agent, the natural rubber foams are also relatively expensive.
The art also discloses elastomeric adhesive compositions which may be combined into a laminar construction having elastic properties. For example, U.S. Pat. No. 5,032,120, issued to Freeland, et al. on Jul. 16, 1991, discloses an improved leg cuff and a hot-melt elastomeric composition designated 198-338 (Findley Adhesives, Inc., of Wauwatosa, WI) as being particularly well suited for the construction of the central laminate of a diaper. Other elastomeric adhesive compositions and constructions employing same have been disclosed in U.S. Pat. Nos. 4,418,123 (Nov. 29, 1983); 4,259,220 (Mar. 31, 1981); and 4,543,099 (Sep. 24, 1985); each issued to Bunnelle, et al.
The adhesive compositions noted above possess a multiplicity of shortcomings which have detracted from their usefulness, particularly in disposable absorbent articles. For example, the adhesive composition 198-338 has a thin film holding strength, i.e., an elastomeric retention when elongated, which rapidly decreases over time, thereby reducing the usefulness of this particular adhesive composition in disposable absorbent garments. In addition, this adhesive composition possesses an unusually long recovery time, i.e., the time it takes for the adhesive to retract to its original length following elongation. The elastomeric adhesive formulations disclosed in the Bunnelle, et al., patents possess a viscosity in excess of one million centipoise at 325.degree. F. Consequently, these adhesive compositions can only be applied by utilizing very expensive manufacturing machinery such as extruders and the like. Further, this high viscosity slows the speed of production lines using conventional manufacturing machinery, thereby increasing the manufacturing costs of disposable garments employing these compositions. In addition, the adhesive compositions of Bunnelle, et al. do not appear to possess the level of adhesion which is necessary for the construction of disposable absorbent garments. Moreover, these compositions do not appear to provide for a convenient and expeditious means by which adhesion can be adjusted without affecting their elastomeric properties.
U.S. Pat. No. 4,731,066, issued to Korpman on Mar. 15, 1988, discloses an elastic laminated disposable diaper having a liquid-impermeable backing which is produced from an initially molten extruded elastic film. The film formers can be extruded as a foam as well as a continuous film, and include pressure-sensitive adhesive materials. However, the pressure-sensitive adhesives disclosed by Korpman would be expected to possess a very high viscosity even at elevated temperatures. Consequently, these compositions, like the compositions of the foregoing Bunnelle patents, would be expected to require very expensive manufacturing equipment (e.g., extruders) and to suffer from low production speeds using conventional equipment. In addition, the structures of Korpman are limited by the extensibility of the backing and/or facing fabric.
Thus there is a continuing need to elasticize absorbent articles in a manner which provides the advantages of elastic components comprising foams without the disadvantages of elastic components known heretofore. Thus, it is an object of the present invention to provide foamed elastic components utilizing less expensive raw materials. It is a further object of the present invention to provide an elastomeric foam that can be formed on-line and that does not require, or requires only reduced amounts of external bonding agents and/or more economical bonding agents for incorporation into absorbent articles. It is a further object of the present invention to provide such foams which may be used to elasticize entire panels of a disposable garment, or alternatively, discrete areas thereof. It is a further object of the present invention to provide a method of elasticizing absorbent articles in a direct manner without waste. Thus it is an object of the present invention to provide a foam which can be formed on-line in a pattern or shape. Another object of the present invention is to provide elastic foams which may be formed into a sheet or other shapes utilizing relatively inexpensive manufacturing techniques or devices, and further which may be formed in a relatively short production time. Yet another object of the present invention is to provide foams having properties desirable for use in absorbent articles, e.g., a relatively high elastomeric retention, a relatively short recovery time, and good adhesion to components typically used therein.
It is a further object of the present invention to provide elastic structures having both a low basis weight and physical properties suitable for use in absorbent articles, e.g., a specified caliper (i.e., loft or thickness), compressibility, resilience, and force of elongation. Yet another object of the present invention is to provide an absorbent article having sustained dynamic fit about the waist of the wearer and improved resistance to leakage during use.
These and other objects of the present invention will be more readily apparent when considered in reference to the following description and when taken in conjunction with the accompanying drawings.